Date
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AP900 DEC sawtooth guiding
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Anis Mo
Hi All, I have a used AP900 mount and I finally got it setup last night for a test run. I have updated the control panel CP3 chip to latest V2 chip.
I connected the mount using AP ASCOM v2 driver and SGP and PHD2. I was hoping to try Pempro to do PE traning but I dont have Maxim which apparently is needed for that software to use my CCD. I need to get back to this once I figure out the DEC i
I did Polar alignment using Polemaster and after connecting the mount with SGP and PHD2, I did PHD2 calibration and let it guide. The guiding was pretty good (under 0.5 arcsec/px in both DEC and RA - I had Tak FSQ108 with 0.73 reducer loaded).
However, when SGP did a dither, the DEC started to go into huge sawtooth pattern (7'' swings with regular interval as the PHD2 tries to get it back). I could see the guide star jump between two points. If I stop and restart guiding, it will run properly again until another dither pulse. I tried changing min-mo, guide algorithm, dropped aggressiveness all the way to 5 but this problem seems to be there.
I am wondering if there is a mechanical adjustment (remesh?) that is needed (since it was transported). I read the AP documentation that has instructions to check if the axis has play and if I try to move the dec axis (with clutches engaged) I dont feel much play (may be a tiny amount ).
Any thing else I should be looking for? Regards Anis |
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blwelty75
Make sure you don't have dec backlash compensation on in your mount or phd2.
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Anis Mo
Yes, I made sure the "Use Backlash Comp" option was not checked in PHD2
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Roland Christen
Sounds like improper calibration. What are your parameter numbers for Dec? What is your pixel scale in Dec?
If the calibration parameter number in Dec is too small, you will indeed get overshoot and back/forth oscillation.
Rolando
-----Original Message-----
From: anismo@... [ap-gto] To: ap-gto Sent: Thu, Sep 22, 2016 8:13 am Subject: [ap-gto] AP900 DEC sawtooth guiding Hi All,
I have a used AP900 mount and I finally got it setup last night for a test run. I have updated the control panel CP3 chip to latest V2 chip.
I connected the mount using AP ASCOM v2 driver and SGP and PHD2. I was hoping to try Pempro to do PE traning but I dont have Maxim which apparently is needed for that software to use my CCD. I need to get back to this once I figure out the DEC i
I did Polar alignment using Polemaster and after connecting the mount with SGP and PHD2, I did PHD2 calibration and let it guide. The guiding was pretty good (under 0.5 arcsec/px in both DEC and RA - I had Tak FSQ108 with 0.73 reducer loaded).
However, when SGP did a dither, the DEC started to go into huge sawtooth pattern (7'' swings with regular interval as the PHD2 tries to get it back). I could see the guide star jump between two points. If I stop and restart guiding, it will
run properly again until another dither pulse. I tried changing min-mo, guide algorithm, dropped aggressiveness all the way to 5 but this problem seems to be there.
I am wondering if there is a mechanical adjustment (remesh?) that is needed (since it was transported). I read the AP documentation that has instructions to check if the axis has play and if I try to move the dec axis (with clutches engaged) I dont feel much play (may be a tiny amount ).
Any thing else I should be looking for?
Regards
Anis
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Roland Christen
Make sure that the backlash setting in the keypad is also set to zero. Again, what is your parameter number for Dec? What is your guider pixel scale?
Rolando
-----Original Message-----
From: anismo@... [ap-gto] To: ap-gto Sent: Thu, Sep 22, 2016 11:01 am Subject: [ap-gto] Re: AP900 DEC sawtooth guiding Yes, I made sure the "Use Backlash Comp" option was not checked in PHD2 |
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Anis Mo
Hi Rolando
I dont have keypad connected to the system. It is only connected to the computer. ASCOM v2 and SGP The PHD2 settings are 1. Camera pixel size - 8.62 micron (Lodestar x2) 2. Focal length - 382mm (Connected via OAG , so FSQ106 with 0,73 reducer) I did calibration few times to be sure with calibration steps of 500ms (as well as let PHD2 calculate based on DEC). The calibration always completed without any issue I also tried with Hystersis as well as resist switch DEC algorithm, as well as with different aggressiveness (all the way to lowest possible aggressiveness). Every one of these times, it will guide properly if I start the guiding but once it receives the dither pulse, the star will start jumping between two points and never settle. (almost same amplitude) Here is one screenshot that I took when it was running ok: http://dev1.codelathe.com/url/5pt30yvcupt3 The DEC always stayed below the 0 line.. not sure if I have PA misalignment (I did PA using polemaster and was able to get it calibrated pretty well as per that software). Thanks! Anis |
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Anis What is your dither setting in SGP? Don Anderson From: "anismo@... [ap-gto]" To: ap-gto@... Sent: Thursday, September 22, 2016 7:13 AM Subject: [ap-gto] AP900 DEC sawtooth guiding Hi All, I have a used AP900 mount and I finally got it setup last night for a test run. I have updated the control panel CP3 chip to latest V2 chip. I connected the mount using AP ASCOM v2 driver and SGP and PHD2. I was hoping to try Pempro to do PE traning but I dont have Maxim which apparently is needed for that software to use my CCD. I need to get back to this once I figure out the DEC i I did Polar alignment using Polemaster and after connecting the mount with SGP and PHD2, I did PHD2 calibration and let it guide. The guiding was pretty good (under 0.5 arcsec/px in both DEC and RA - I had Tak FSQ108 with 0.73 reducer loaded). However, when SGP did a dither, the DEC started to go into huge sawtooth pattern (7'' swings with regular interval as the PHD2 tries to get it back). I could see the guide star jump between two points. If I stop and restart guiding, it will run properly again until another dither pulse. I tried changing min-mo, guide algorithm, dropped aggressiveness all the way to 5 but this problem seems to be there. I am wondering if there is a mechanical adjustment (remesh?) that is needed (since it was transported). I read the AP documentation that has instructions to check if the axis has play and if I try to move the dec axis (with clutches engaged) I dont feel much play (may be a tiny amount ). Any thing else I should be looking for? Regards Anis |
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Roland Christen
Still no information to work with. need to know the calibration parameter numbers after you do a calibration run.
Example: If pixel scale is 1 arc sec per pixel, then Dec movement would be 15 pixels per second. This parameter (15) is then used to determine the amount of move command that is sent to the mount. Therefore if the error is 1 pixel, the mount would be commanded to move 1/15 sec at 1x guide rate. This also means that the loop gain is 100%, which means that a 1 pixel error is compensated by a 1 pixel move command.
Knowing the pixel scale and the calibration result (parameter number obtained after calibration run) allow you to know if the loop gain is 100% or not.
If calibration number is wrong, your resultant loop gain might be more than 100%. If the parameter number obtained after a cal. run is only 7.5 rather than 15 in the above example, then for every 1 arc second position error the mount gets a 2 arc second (1/7.5 second) move command. Loop gain is now 200%. So, the net result is overshoot after every error with the axis constantly bobbling back and forth. The smaller the number relative to the correct number, the larger the overshoot.
Rolando
-----Original Message-----
From: anismo@... [ap-gto] To: ap-gto Sent: Thu, Sep 22, 2016 12:30 pm Subject: [ap-gto] Re: AP900 DEC sawtooth guiding Hi Rolando I dont have keypad connected to the system. It is only connected to the computer. ASCOM v2 and SGP
The PHD2 settings are
1. Camera pixel size - 8.62 micron (Lodestar x2)
2. Focal length - 382mm (Connected via OAG , so FSQ106 with 0,73 reducer)
I did calibration few times to be sure with calibration steps of 500ms (as well as let PHD2 calculate based on DEC). The calibration always completed without any issue
I also tried with Hystersis as well as resist switch DEC algorithm, as well as with different aggressiveness (all the way to lowest possible aggressiveness).
Every one of these times, it will guide properly if I start the guiding but once it receives the dither pulse, the star will start jumping between two points and never settle. (almost same amplitude)
Here is one screenshot that I took whe
n it was running ok: http://dev1.codelathe.com/url/5pt30yvcupt3
The DEC always stayed below the 0 line.. not sure if I have PA misalignment (I did PA using polemaster and was able to get it calibrated pretty well as per that software).
Thanks!
Anis
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Anis Mo
Hi Rolando
Appreciate your help! Here are some data I pulled from the log after calibration ============================ Calibration Begins at 2016-09-21 21:49:01 Equipment Profile = AP900_LODESTARX2 Camera = Starlight Xpress Lodestar Guider (ASCOM) Exposure = 8000 ms Pixel scale = 4.60 arc-sec/px, Binning = 1, Focal length = 386 mm Mount = AstroPhysicsV2, Calibration Step = 1200 ms, Assume orthogonal axes = no Dec = 58.5 deg, Hour angle = -5.14 hr, Pier side = West, Rotator pos = N/A Lock position = 56.602, 134.484, Star position = 56.602, 134.484, HFD = 3.36 px West calibration complete. Angle = -137.3 deg, Rate = 1.817 px/sec North calibration complete. Angle = 132.7 deg, Rate = 3.438 px/sec ================================ Guiding Begins at 2016-09-21 22:00:34 Dither = both axes, Dither scale = 1.000, Image noise reduction = none, Guide-frame time lapse = 0, Server enabled Pixel scale = 4.60 arc-sec/px, Binning = 1, Focal length = 386 mm Search region = 15 px, Star mass tolerance = 50.0% Equipment Profile = AP900_LODESTARX2 Camera = Starlight Xpress Lodestar Guider (ASCOM), gain = 95, full size = 752 x 580, no dark, no defect map, pixel size = 8.6 um Exposure = 10000 ms Mount = AstroPhysicsV2, connected, guiding enabled, xAngle = -137.3, xRate = 1.817, yAngle = -227.3, yRate = 3.438 X guide algorithm = Hysteresis, Hysteresis = 0.100, Aggression = 0.100, Minimum move = 0.200 Y guide algorithm = Hysteresis, Hysteresis = 0.100, Aggression = 0.050, Minimum move = 0.200 Backlash comp = disabled, pulse = 0 ms Calibration step = phdlab_placeholder, Max RA duration = 2500, Max DEC duration = 2500, DEC guide mode = Auto RA Guide Speed = 15.0 a-s/s, Dec Guide Speed = 15.0 a-s/s, Cal Dec = 58.5, Last Cal Issue = None, Timestamp = 9/21/2016 9:54:46 PM Dec = 58.5 deg, Hour angle = -4.95 hr, Pier side = West, Rotator pos = N/A ============================== I have the whole PHD2 log (I did multiple calibration as well as guide/dither with different settings) if that will be useful Regards Anis |
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bw
Hi Anis. I think you're posting to the wrong forum, the folks here aren't very familiar with PHD2. If you post your question over here: Google Groups
and include your guide log, we'll probably be able to sort out your problem. In the meantime, get on the latest release of PHD2 and read the help file regarding the Guiding Assistant and how to measure your Dec backlash. Good luck, Bruce W. |
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Anis Mo
Thanks Bruce, That is a good point. I wasn't sure if this is a mount related issue vs PHD2 issue. I guess the fact that the normal guiding working probably indicates something settings related. I am also planning to run the pulse guide test tonight as well and see if I can get some additional details.
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Anis Mo
Additional info: Instead of the PHD log, I have it loaded in PHDLab
Here is a 13.5 minute with normal guiding: http://dev1.codelathe.com/url/zlk2xugsghth Here is the case showing the "sawtooth": http://dev1.codelathe.com/url/y3twje1dnr2i |
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Roland Christen
That kind of sawtooth guiding is very indicative of loop gain greater than 100% due to faulty calibration parameters. It says something like "send a 2 arc second correction for a 1 arc second error". It's called overcorrection or Loop Gain > 100%, etc. The software is misinterpreting the actual error and sending a very much larger correction signal to the mount. I'm guessing at least a 200% overcorrection, possibly due to interpreting a wrong binning setting or a wrong calibration parameter.
Not being familiar with PHD, I cannot begin to guess where the error might be. In Maxim, it is easy to see the actual calibration numbers, and you can even modify them to the correct value for 100% stable operation.
It's almost like the software is interpreting the smaller RA parameter number to be applied to the Dec axis. That is the danger of calibrating away from the celestial equator where the two numbers (RA and Dec) would be the same. If they are not the same, then you know right away that your calibration was not accurate.
Rolando
-----Original Message-----
From: anismo@... [ap-gto] To: ap-gto Sent: Thu, Sep 22, 2016 2:59 pm Subject: Re: [ap-gto] Re: AP900 DEC sawtooth guiding Additional info: Instead of the PHD log, I have it loaded in PHDLab Here is a 13.5 minute with normal guiding: http://dev1.codelathe.com/url/zlk2xugsghth
Here is the case showing the "sawtooth": http://dev1.codelathe.com/url/y3twje1dnr2i
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Anis Mo
Thanks Rolando! I think I am getting a sense of things to check on now.
I have a bunch of stuff to check with guiding parameters (Bruce also pointed to me few things to work on). I will get this done the next chance I get (probably next week) and hopefully have better results. |
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bw
The log shows the calibration was near-perfect. PHD2 does a bunch of sanity-checks on calibration and generates alerts when things don't look right - none of that happened. I suspect there's a non-zero Dec backlash compensation setting in the mount, and that's what needs to be dealt with next. Since this is a second-hand mount, Anis doesn't have any way to know what might have been programmed by the original owner.
Cheers, Bruce |
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Steve Reilly
If he doesn’t have the hand controller the driver, I would think, should show the setting for sure.
Steve
From: ap-gto@... [mailto:ap-gto@...]
Sent: Thursday, September 22, 2016 11:21 PM To: ap-gto@... Subject: Re: [ap-gto] Re: AP900 DEC sawtooth guiding
The log shows the calibration was near-perfect. PHD2 does a bunch of sanity-checks on calibration and generates alerts when things don't look right - none of that happened. I suspect there's a non-zero Dec backlash compensation setting in the mount, and that's what needs to be dealt with next. Since this is a second-hand mount, Anis doesn't have any way to know what might have been programmed by the original owner. |
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Horia
Hi Anis,
Your PHD2 log looks very much like the system is trying to compensate some nonexistent backlash: As in PHD the backlash compensation is inactive, you should check if it is also set to 0 in the AP ASCOM v2 driver. For that, go to the AP-Driver setup (Telescope setup / Advanced Options) and have a look at the RA-Backlash and DEC-Backlash values. What values do you have there? They should both be set to 0. This should take care of the “saw tooth” behavior. After that and given the fact that the mount is actually reacting extremely smooth, there is some fine tuning to be done. But first things first. Regards, Horia Von: ap-gto@... [mailto:ap-gto@...] Gesendet: Freitag, 23. September 2016 04:08 An: ap-gto@... Betreff: Re: [ap-gto] Re: AP900 DEC sawtooth guiding Thanks Rolando! I think I am getting a sense of things to check on now. I have a bunch of stuff to check with guiding parameters (Bruce also pointed to me few things to work on). I will get this done the next chance I get (probably next week) and hopefully have better results. [Non-text portions of this message have been removed] |
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bw
I kind of doubt it. According to the published AP command protocol, there's no way to read these values from the mount firmware. You can only set them. There are actually quite a number of these "write-only" properties that have to be dealt with in a driver. Maybe AP has added these capabilities in later versions of the firmware without documenting them, but since the mount is used, it doesn't seem likely to me that it would have the latest and greatest software. Let's wait and see what happens.
Bruce |
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Ray Gralak
Bruce,
I kind of doubt it. According to the published AP command protocol, there's noI think he meant that to check the backlash values in the hand controller because the HC will initialize the mount with them. On power up, I think the backlash values default to 0. The values can later be set by the HC, driver, APCC, or other application. BTW, the CP4's do not have backlash settings at all so they are always 0. -Ray Gralak Author of APCC (Astro-Physics Command Center): http://www.astro-physics.com/index.htm?products/accessories/software/apcc/apcc Author of PEMPro: http://www.ccdware.com Author of Astro-Physics V2 ASCOM Driver: http://www.gralak.com/apdriver Author of PulseGuide: http://www.pulseguide.com Author of Sigma: http://www.gralak.com/sigma -----Original Message----- |
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Joe Zeglinski
Hi Ray,
Since the “Backlash is always zero – for CP4” ... would
it be possible to grey-out Backlash settings in the ASCOM-V2 driver Advanced
setup panel? Of course, that requires the user to select CP4 in the controller
panel ID box first.
The Backlash topic comes up fairly often, perhaps this
might lead to less confusion about exactly which software has backlash
“still” set. It is appropriate for Backlash compensation to be centralized in
the ASCOM driver rather than spread among any apps. It seemed to be the best
place to provide compensation, until the user had either time or the opportunity
to remesh the gears.
Actually, I am curious how backlash compensation is now
handled by the CP4 firmware, since backlash is a “mechanical” problem and more
dependent on the gear mating improvements in the new mounts. I thought this
would be related to the driver’s Mount Type selection box instead. Then again,
old mounts can also have newer gear box retrofits, so that wouldn’t work.
Joe
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